Light quarks beyond chiral limit

We discuss the instanton vacuum based Diakonov - Petrov (DP) QCD effective action and propose the improved effective action, which is derived on the basis of the Lee-Bardeen results for the quark determinant in an instanton field. The improved effective action (in contrast to the DP action) provides a proper account of current quark masses, which is particularly important for strange quarks. This action is successfully tested by the calculations of the quark condensate, masses of the pseudoscalar meson octet, and by axial-anomaly low-energy theorems